In the field of electronics, it has long been desirable to be able to identify pertinent processing and test information about particular semiconductor circuits or chips. In some instances, reworked parts are not satisfactory for a customer's use. In memory arrays implemented with redundancy, some customers desire to know whether and where redundancy was used because of pattern sensitivity and other considerations. For some applications, particularly where military or other specialized specifications are to be met, it is useful to know whether certain visual inspections or tests have been performed on the part, or what the results are of critical dimension measurements, such as layer thickness, or other parameter measurements made during the processing of the lot of wafers from which the part is made. However, prior to the present invention, obtaining pertinent and useful processing and test details, such as wafer number, lot number, processing parameters, special visual and test results and manufacturing network data has been difficult if not impossible to obtain because after processing, testing and packaging it is difficult to keep track of particular manufacturing lots in inventory, and records are often fragmented or nonexistent.
Inspections of the package do not directly reveal this information, and are frequently complicated by the presence of adjacent circuitry, lack of identifying marks on the package, coatings or other coverings placed over the chip to assure circuit integrity and other reasons. Even where helpful information such as assembly date is provided on the package, the underlying wafer processing records are often unlocatable, inaccurate or incomplete. Inspections of the chip itself are difficult because of all of the foregoing and most often do not reveal pertinent information. In any event, the package is not intended to be removable, and such removal normally destroys the device.
As a result, there has been a need for a method and device whereby processing and test information could be determined with certainty without the need for reliance on incomplete or difficult to trace paperwork.